The long term objective of this project is to analyze the sequence of changes that lead to the maturation of the neurotransmitter systems of the cerebral cortex during a critical period of postnatal development when the cortex is subject to systemic and peripheral activity-dependent plasticity. Such plasticity appears to depend in large part on the development of normal neurotransmitter function in the cortex. At every stage of this, there are windows of vulnerability during which perturbations can have long lasting consequences. The immediate aims of the project are focused on the somatosensory cortex of mice and on the inhibitory neurotransmitter, GABA and the excitatory neurotransmitter, glutamate. A combination of electron microscopy, immunocytochemistry, axonal transport, receptor autoradiography and in situ hybridization histochemistry will be used in normal animals and in animals subjected to perturbations of facial vibrissae in the critical period to chart changes in synapse distribution and gene expression over time.